1. Field of the Invention
The present invention relates to a light source of a non-self-luminous display device, and more particularly to a liquid crystal display device having a backlight which includes a light guide plate and uses an LED as a light source.
2. Background Art
Recently, the liquid crystal display device has been popularly used as a display device. Particularly, the liquid crystal display device is used as a display part of portable equipment because of a reduced thickness, a reduced weight and small electric power consumption.
However, the liquid crystal display device is not self-luminous and hence, the display device requires an illumination means. In general, as a lighting device which is used for the liquid crystal display device, a flat lighting device referred to as a backlight is popularly used. Conventionally, although a cold cathode fluorescence light tube has been used as a light emitting element (also referred to as a light source) of the backlight, an LED (light emitting diode) has been also recently used as the light emitting element.
The backlight includes a plate-like light guide plate. The light guide plate is made of a light-transmissive resin material or the like. The light which is incident on the light guide plate from the light emitting element transmits the inside of the light guide plate. Reflection and diffusion members such as grooves, projections or printed materials are formed on the light guide plate, and the light which transmits in the inside of the light guide plate is radiated toward a liquid-crystal-display-device side by the reflection and diffusion members.
In using an LED as the light emitting element, the LED is a point light source and hence, there arises a drawback that it is difficult to uniformly radiate light from the light guide plate. Accordingly, for example, JP-A-2004-286777 and the like propose a technique for uniformly diffusing light in the vicinity of the LED. That is, these documents disclose the constitution in which a light guide plate is formed along a side surface of the LED and the light is incident on the light guide plate from the side surface of the LED. Further, JP-A-2004-186131 discloses a light guide plate having two thicknesses.